The present invention relates to a method for the control of a magnetic disk unit and to a magnetic disk unit using such a method. Specifically, it relates to a technique which can be effectively applied to the control of a magnetic disk unit having a load/unload system.
In recent years, magnetic disk units have been designed to have a higher recording density and less surface roughness, and the flying heights of magnetic heads are getting lower. Therefore, in a conventional magnetic disk unit of the contact-start-stop type, wherein a magnetic head stays on a magnetic disk when the rotation of the magnetic disk is stopped, adsorption (sticking) is apt to occur between the magnetic disk and the magnetic head, which sometimes makes it difficult to start up the magnetic disk.
As one of the solutions for this technical problem, a system called a load/unload system has been developed, in which the magnetic head is loaded on and unloaded from the magnetic disk in a controlled manner. When the magnetic disk is stopped, this system keeps the magnetic head away from the magnetic disk (unloaded state). Further, when the disk is rotating so as to write and read data, the system places (loads) the magnetic head at a position above the magnetic disk so as to be in a flying state.
Now, a typical example of a load/unload operation of a load/unload system will be described.
First, a load operation of the load/unload system will be described. When the unit is stopped, the magnetic head is in a retreated state located away from the magnetic disk and is supported by a lift tab attached to the magnetic head moves on a ramp (sloping path). When the unit is turned on, the rotation of the magnetic disk is started by a spindle motor. When the rated rotational speed has been reached, the magnetic head is displaced laterally from its retreated state and descends the ramp while being guided by the lift tab and takes a position (loaded) above the magnetic disk so as to be in a flying state.
Next, an unload operation will be described. During the disk rotation, when an instruction to stop the unit is issued, the magnetic head, which is disposed at a flying position above the magnetic disk, is guided laterally to a point where the lift tab is caused to slide along the ramp, through a moving action of an actuator, thereby to ascend the ramp, causing it to be displaced from the magnetic disk, after which the motor is stopped.
Now, a subambient pressure slider in the magnetic disk will be described. The subambient pressure slider has a positive-pressure generating portion and a negative-pressure generating portion on a flying surface opposing the magnetic disk. Further, it flies above the disk according to a proper balance between itself and the load.
When unloading, the lift tab runs onto the ramp so that the magnetic head tends to be held at a position away from the magnetic disk. At this time, since a negative-pressure portion exists in part of the flying surface of the slider, a reactive force in the direction of attracting the slider to the surface of the magnetic disk is produced to break the flying posture. Further, in the course of unloading, before he left tab of the magnetic head runs onto the ramp, the magnetic head collides with the magnetic disk, thereby increasing the possibility of causing abrasion and damage to the magnetic disk and the magnetic head, which has been a problem to be solved technically.
Further, to reduce the data-access time, when using a 3.5-inch magnetic disk unit at a rotational speed higher than 10,000 rpm, instead of a conventional 2.5-inch magnetic disk unit at 4,200 rpm, the impact of the collision between the magnetic head and the magnetic disk is intensified, thereby increasing the possibility of causing abrasion and damage to the magnetic disk and the magnetic head when they contact each other.
The solution to the problem of avoiding damage when loading and unloading may be to decrease the moving speed of the magnetic head. However, this brings about another technical problem, such as prolongation of the time for loading and unloading.
It is an object of the present invention to provide a magnetic disk unit in which damage to a magnetic head and a magnetic disk, etc. caused by contact or collision therebetween during a load/unload operation is reduced, as well as a control technique therefor.
In a method of control of a magnetic disk unit, which comprises a magnetic disk, a head for writing and reading data to and from the magnetic disk, an actuator positioning the head on the magnetic disk, and a load/unload system for unloading the head by moving the head away from the magnetic disk and for loading the head by bringing the head on the magnetic disk, at least either loading or unloading is carried out at a second rotational speed, which is lower than a first rotational speed at which writing and reading to and from the magnetic disk by the head are carried out.
Also, according to the present invention, in a method of control of a magnetic disk unit, which comprises a magnetic disk, a head for writing and reading data to and from the magnetic disk, an actuator for positioning the head on the magnetic disk, a load/unload system for unloading the head by taking the head away from the magnetic disk and for loading the head by bringing the head on the magnetic disk, a control logic is provided which executes at least either loading or unloading at a second rotational speed, which is lower than a first rotational speed at which writing and reading to and from the magnetic disk by the head is carried out.
More specifically, as an example, the rotational speed of the magnetic disk when loading/unloading the head is set to be a half to one-tenth of the rotational speed used for a usual R/W operation. Further, as a head slider making up part of the magnetic head, a shallow dual-step subambient pressure slider is used, whose flying height gets higher as a result of the lower disk rotational speed during loading/unloading. Also, the upper limit of the moving speed of the magnetic head during loading/unloading is set to be 0.1 m/s.